A personal computer (PC) display typically shows a stack of application windows corresponding to different types of work a user may be doing (for example, word processing, e-mail, spreadsheet, video, etc.), with the currently active application window at the top of the stack, thus appearing closest to the user. When a user changes from one activity to another, these windows are re-composed into a new desktop image, bringing a new application window to the fore.
Future PC product plans call for composing the application windows using three-dimensional (3D) animation techniques to provide the user with a richer visual experience where the animations move smoothly. To make the animations move smoothly, they must be free from jerkiness that can be caused if the desktop image is not composed rapidly enough. Unfortunately, composing a PC desktop image at sufficiently high rates requires excessive amounts of graphics memory bandwidth, which increases costs to levels that may be unsustainable in products targeting the mobile and low cost PC markets.
Conventionally, to deal with inadequate computational or memory resources, frames are simply dropped. Since image information representing original content is discarded, the result often is animation that is jerky in appearance, similar to animated video often seen on personal computers today. This frame skipping may cause the video frame-rate to drop below the frame rate desired to perceive smooth motion. As a result, low bit rate video may at times look jerky to the user.